Flexible disc obturator for a cannula assembly

ABSTRACT

An obturator for a cannula includes an elongate member and a flexible disc. The cannula has proximal and distal ends and a lumen extending therebetween. The distal end of the cannula has a circular cross-section. The cannula also includes a first portion having a non-circular cross-section and at least one fluid aperture formed adjacent the distal end. The flexible disc of the obturator is coupled to a distal end of the elongate member, both of which are adapted to be telescopically received in the lumen of the cannula. The flexible disc is configured to restrict the flow of fluid, entering the at least one fluid aperture, through the lumen.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a division of Application Ser. No. 09/012,520, filedJan. 23, 1998 now U.S. Pat. No. 6,447,484, incorporated herein byreference in its entirety, which is a continuation-in-part ofApplication Ser. No. 08/780,995, filed Jan. 9, 1997, now U.S. Pat. No.5,817,071.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to cannulas and, more particularly, to a cannulawhich is oval-shaped in cross-section and therefore ideally suited foruse in minimally invasive surgical procedures.

2. Description of the Related Art

Cannulas have a wide variety of applications during surgical procedures.For example, in coronary surgery, venous and arterial cannulas are usedto conduct blood between the body and bypass equipment. Cannulas areused to conduct cardioplegia solution for both antigrade and retrogradesolution administration, and cannulas are also used as vents, sumps, andfor chest tube fluid suction. The structure for these known cannulasgenerally comprises a cannula body which is circular in cross-sectionand has at least one lumen extending therethrough which is similarlycircular in cross-section. Examples of these structures are seen in U.S.Pat. No. 4,639,252, 4,129,129 and U.S. Pat. No. 5,395,330.

A recent trend in surgical procedures is to minimize the size of theaccess apertures formed in the chest cavity. These procedures includemini-sternotomy and minimally invasive cardiac surgery. In each of theseprocedures, the goal is to reduce the size of the aperture in the chestwall. One problem in achieving this goal is the size, geometry, andspace requirements for the instruments, cannulas, and the like whichmust pass through the reduced size apertures.

SUMMARY OF THE INVENTION

The cannula according to the invention overcomes the problems of theprior art by providing a cannula having a prescribed geometry, whichmore efficiently occupies the space of the aperture without adverselyaffecting the fluid rate therethrough, and an obturator for use with thecannula.

In accordance with one embodiment of the invention, an obturator for acannula is provided. The cannula has proximal and distal ends, and alumen extending therebetween. The distal end of the cannula is circularin cross-section. The cannula further includes a first portion having anon-circular cross-section and at least one fluid aperture formedadjacent the distal end. The obturator includes an elongate member and aflexible disc which is coupled to a distal end of the elongate member.The elongate member and flexible disc of the obturator are adapted to betelescopically received in the lumen of the cannula, and the flexibledisc is configured to restrict the flow of fluid, entering the at leastone fluid aperture, through the lumen.

In another embodiment of the invention, a cannula assembly includes acannula and an obturator. The cannula has proximal and distal ends, alumen, a first portion, and at least one fluid aperture as describedabove. The obturator, which is telescopically received in the cannulalumen, includes an elongate member and a flexible disc. The flexibledisc substantially restricts the flow of fluid, entering the at leastone fluid aperture, through the lumen, when the obturator is fullyinserted in the cannula.

The invention is also directed to a method of positioning a fluidconducting cannula in a body. The method includes the steps of providinga cannula, such as that described above, and inserting an obturator inthe lumen of the cannula. The obturator includes an elongate member anda flexible disc coupled to a distal end of the elongate member. Theflexible disc substantially restricts the flow of fluid, entering the atleast one fluid aperture, through the lumen of the cannula. The methodfurther includes the steps of providing a percutaneous aperture in abody, inserting the distal end of the cannula in the percutaneousaperture, and positioning the cannula so that the first portion thereofextends through the percutaneous aperture.

The invention is further directed to a method of positioning a fluidconducting cannula in a body, including the step of providing apre-assembled cannula assembly. The pre-assembled cannula assembly hasincludes a cannula, as described above, and an obturator disposed in thelumen of the cannula. The method further includes the steps of providinga percutaneous aperture in a body, inserting the distal end of thepre-assembled cannula assembly into the body through the percutaneousaperture, and positioning the cannula so that the first portion extendsthrough the percutaneous aperture.

Other advantages of the invention will become apparent from the detaileddescription given hereinafter. It should be understood, however, thatthe detailed description and specific embodiments are given by way ofillustration only, since, from this detailed description, variouschanges and modifications within the spirit and scope of the inventionwill become apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawings inwhich:

FIG. 1 is a perspective view of a venous cannula assembly wherein atleast a portion of the cannula body is oval in cross-section;

FIG. 2 is a cross-sectional view taken generally along the line 2—2 ofFIG. 1 showing the oval cross-section of the cannula body;

FIG. 3 is a plan view of a patient showing a cannula according to theinvention passing through a mini-thoracotomy;

FIG. 4 is a perspective view of a second embodiment of the cannulawherein at least two portions of the cannula body are oval incross-section and the oval sections are not aligned with one another;

FIG. 5 is a cross-sectional view taken generally along the line 5—5 ofFIG. 4 showing the oval cross-sections of the second embodiment of thecannula body;

FIG. 6 is a plan view of a second embodiment of the obturator for thecannula assembly;

FIG. 7 is a plan view of a third embodiment of the obturator;

FIG. 8 is a partial cross-sectional view of the cannula of FIG. 1 with afourth embodiment of the obturator for the cannula assembly, showing theobturator fully inserted in the cannula;

FIG. 9 is a cross-sectional view taken generally along the line 9—9 ofFIG. 8;

FIG. 10 is a partial cross-sectional view of the cannula of FIG. 1showing the fourth embodiment of the obturator partially retracted;

FIG. 11 is a cross-sectional view taken generally along the line 11—11of FIG. 10;

FIG. 12 is a plan view of the obturator shown in FIGS. 8-11 andincluding a malleable, stainless steel sleeve; and

FIG. 13 is a cross-sectional view taken generally along the line 13—13of FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings and to FIGS. 1 and 2 in particular, a firstembodiment of the cannula assembly according to invention is shown. Thefirst embodiment of the cannula assembly 12 comprises a cannula 14 andan obturator 16 which is selectively, telescopically received in thecannula 14. The cannula 14 comprises a cannula body 18 having a proximalend 20, a distal end 22, and a lumen 24 extending between the proximaland distal ends. A conventional luer connector 26 is preferably providedon the proximal end 20, and the distal end 22 preferably includes atleast one fluid inlet aperture for the receipt of fluid into the lumen.A helically wound reinforcing spring 38 is preferably, integrally formedinto the cannula body 18. The cannula seen in FIGS. 1 and 2 includes afirst set of fluid apertures 28 formed immediately adjacent the distalend 22 and a second set of apertures 30 formed a spaced distanceproximally from the distal end. This structure is ideally suited for useas a venous cannula during a cardiac surgical procedure.

One unique feature of the cannula assembly according to the invention isthat at least a portion of the cannula body 18 is noncircular. Thisfirst non-circular portion 32 is preferably oval in cross-section and isdefined by a major cross-sectional axis 34 and a minor cross-sectionalaxis 36. As will be described further below, the incorporation of anon-circular portion 32 makes the cannula assembly according to theinvention ideally suited for use in minimally invasive cardiac surgicalprocedures.

The obturator 16 comprises a proximal end 48 and a distal end 50. Theobturator is adapted to be slidably, telescopically received inside thelumen 24 of the cannula 14. When the obturator is fully received insidethe cannula lumen 24, the obturator substantially seals the second setof fluid apertures 30 so that fluid cannot enter the lumen 24 from thefirst set of fluid apertures 28 and then egress into the operation fieldthrough these apertures.

The cannula assembly 12 described above is ideally suited for use as avenous cannula during a coronary surgical procedure similar to thecannula described in U.S. Pat. No. 4,129,129 which is expresslyincorporated herein by reference. In use, the cannula 14, with theobturator 16 fully received therein, is inserted through an appropriateincision into the right atrium and the inferior vena cava. As the distalend 22 of the cannula 14 is inserted into the blood flow passing throughthe right atrium and inferior vena cava, blood will enter the first setof fluid apertures 28, but the obturator 16 will restrict the flow ofblood through the lumen 24 to the second set of fluid apertures 30. Oncethe cannula 14 is properly positioned, the obturator 16 is removed fromthe cannula 14, and the luer connector 26 of the cannula 14 is connectedto a conventional bypass system. With the cannula 14 in this position,blood enters the lumen 24 through both the first and second fluidapertures 28, 30 and is conducted to the bypass machine.

Traditional cardiac surgery is typically performed by a mediansternotomy in which substantially the entire chest cavity is exposed bycutting the full length of the sternum and spreading back the sternumand ribs to expose the entire pericardium. However, a recent trend incardiac surgery is to attempt to minimize the size of the accessapertures formed in the patient's chest using techniques such as a rightor left anterior thoracotomy, mini-sternotomy, and multi-port accessapertures. In each of these procedures, the size of the access apertureformed in the patient's chest is considerably smaller than thetraditional median sternotomy, thereby reducing the complications andpossible side effects associated with such a massive wound. However,reducing the size of the access aperture raises a new set of problemsnot encountered in the conventional median sternotomy, namely,sufficient space for the receipt of all the instruments and equipment.

One limiting factor to reducing the size of the access aperture in anysurgical procedure is the cross-sectional space requirements of thesurgical tools which must be inserted through the access aperture. Thecannula according to the invention is an improvement over the knowncannulas because it more efficiently utilizes the limited space of theaccess aperture without adversely affecting the fluid flowcharacteristics through the cannula.

As seen in FIGS. 1-3, at least a portion 32 of the cannula body 18 isoval in cross-section, and the cannula body 18 is received in an accessaperture 52 formed in the chest wall 54 of the patient 56. In thisexample, the access aperture 52 comprises a right anterior thoracotomy.Preferably, the proximal 20 and distal 22 ends of the cannula 14 arecircular in cross-section while the central portion of the cannula body18 is oval in cross-section. When the oval portion 32 of the cannula ispositioned in the access aperture 52, the available cross-sectional areaof the access aperture 52 is used more efficiently. Preferably, thecannula is positioned so that the minor cross-sectional axis 36 extendsradially inwardly from the sidewall of the access aperture 52. With thisstructure, the cannula 14 extends a minimum distance inwardly toward thecenter of the access aperture 52 thereby utilizing the available spacemore efficiently. If a traditional cannula having a round cross-sectionwith a flow rate potential comparable to the oval-shaped cannulaaccording to the invention were positioned in the access aperture 52,then the diameter of the round cannula would extend farther toward thecenter of the access aperture 52 and utilize the valuablecross-sectional area of the opening far more inefficiently.

While the preferred embodiment of the cannula 14 and cannula assembly 12described above is a venous cannula, it is to be understood that theinvention extends to any cannula inserted into the body through anaccess aperture including but not limited to an arterial cannula, acardioplegia cannula (both retrograde and antigrade), a vent, a sump, ora suction tube. Similarly, FIG. 3 shows use of a cannula in a rightanterior thoracotomy. It is to be understood that the benefits of theinvention can be realized regardless of the particular surgical aperturewhich is created.

FIGS. 4 and 5 show a second embodiment of the cannula according to theinvention. In this embodiment, the cannula 64 also includes a secondnon-circular portion 66. Preferably, the second non-circular portion isoval in cross-section and has a major cross-sectional axis 68 and aminor cross-sectional axis 70 with the major cross-sectional axes 34,68, respectively, of the first and second non-circular portions 32, 66not being parallel to one another and preferably perpendicular to oneanother. With this structure, the first non-circular portion 32 can bepositioned to extend through the access aperture 52 as described above,and the second non-circular portion 66 can be positioned either insidethe body or outside the body in a particular position which requiressignificant bending or deflection of the cannula 64.

A second embodiment of the obturator 76 is shown in FIG. 6. When thecannula is used as a venous cannula during a cardiac surgical operation,it is preferred to include an obturator which substantially seals thesecond set of fluid apertures 30 from the first set of fluid apertures28 during the initial insertion of the cannula 14 in to the blood flow.In the preferred embodiment of the cannula 14, the minor cross-sectionalaxis 36 of the non-circular portion 32 is less than the interiordiameter of the distal end 22 of the cannula 14. Therefore, in order forthe obturator to be telescopically inserted and removed from the lumen,whatever means are incorporated onto the obturator must be pliable orradially expandable to accommodate these diametrical constraints. Inthis embodiment, an expandable member such as a conventional, siliconeballoon 78 is provided on the distal end 50 of the obturator 76. Theobturator 76 comprises a proximal end 80 and a distal end 82. Theballoon 78 is fluidly connected to an inflation lumen 84 which extendsfrom the balloon 78, to the proximal end of the obturator. Preferably, aluer connector 86 is mounted to the terminal end of the inflation lumen84.

The balloon is adapted for inflation from a retracted state as seen inFIG. 6 to an expanded state which extends radially outwardly from theobturator 76 a sufficient distance to substantially seal the second setof fluid apertures 30. In use, the obturator 76 is inserted into thelumen 24 with the balloon 78 in the retracted state. Once the distal end82 of the obturator 76 is received in the lumen 24 so that the balloon78 is positioned immediately adjacent the second set of fluid apertures30, the balloon 78 is inflated through the flow of pressurized fluidthrough the inflation lumen 84 and connector 86. The balloon 78 isinflated a sufficient amount to substantially seal the fluid apertures30. Once the cannula assembly 12 is properly positioned in the bloodflow, the balloon 78 is deflated by removing the pressurized fluid fromthe balloon 78 through the inflation lumen 84 and connector 86. Once theballoon 78 is sufficiently deflated, then the obturator 76 is removedfrom the cannula lumen 24, and the lumen is fluidly connected to thebypass system.

A third embodiment of the obturator 90 is shown in FIG. 7. Similar tothe earlier embodiments, this embodiment of the obturator 90 comprises aproximal end 92 and a distal end 94. However, in this embodiment, anexpandable foam member 96 is mounted on the distal end 94 of theobturator 90. In the relaxed state, the diameter of the foam member 96is slightly larger than the interior diameter of the cannula 14 at thesecond set of fluid apertures 30. Therefore, when the foam member 96 ispositioned immediately adjacent the apertures 30, the foam member willsubstantially seal the apertures 30 from the lumen 24.

In the third embodiment, the foam member 96 is formed from a soft,pliable foam which can easily be compressed by the opposed sidewalls ofthe cannula in the non-circular portion as the obturator 90 passestherethrough. Once the obturator 90 is fully received in the lumen 24,the foam member 96 expands outwardly a sufficient distance tosubstantially seal the fluid apertures 30. Similar to the earlierembodiments, once the cannula assembly 12 is properly positioned, thenthe obturator is telescopically removed from the lumen. As the obturatoris being pulled through the non-circular portions, the opposed sidewallsof the lumen will compress the foam member a sufficient distance topermit passage of the foam member therethrough.

A fourth embodiment of the obturator 100 for a cannula 14 is showngenerally in FIGS. 8-13. As with the earlier embodiments, the obturator100 has a proximal end 102 and a distal end 104. The obturator 100includes an elongate member 106 and a flexible disc 108, which iscoupled to the distal end 104 of the elongate member 106. The flexibledisc 108 is preferably, but not necessarily, thin. In the presentembodiment of the invention, the flexible disc 108 is round and has adiameter substantially equal to the diameter of the lumen 24 at thedistal end 22 of the cannula body 18. However, it should be noted thatthe flexible disc 108 may have a non-circular shape, provided that itsshape corresponds to that of the lumen 24 at the distal end 22. Asillustrated in FIG. 9, when the obturator 100 is fully inserted into thecannula lumen 24, the flexible disc 108 substantially seals the distalend of the lumen 24 to prevent the flow of blood, which enters throughthe first set of fluid apertures 28, from passing through the lumen 24to the second set of fluid apertures 30. After the cannula 14 isinserted into a blood vessel, the obturator 100 is removed, allowingblood to flow through the first and second sets of fluid apertures 28and 30, respectively, and into the lumen 24.

The flexible disc 108 is formed from a durable material which issufficiently flexible that the edges of the disc 108 bend, enabling thedisc 108 to pass through the first non-circular portion 32 of thecannula body 18, as shown in FIG. 10, and is also sufficiently stiff toocclude the distal end 22 of the lumen 24 when the cannula 14, with theobturator 100 inserted therein, is positioned in a body. The flexibledisc 108 is preferably made of polypropylene or polyethylene but mayalso be made of other materials, such as foam, teflon, or otherplastics.

As shown in FIGS. 9 and 11, the flexible disc 108 further includes afeature 109 for allowing air to escape from the proximal end 20 of thecannula 14. Preferably, the feature 109 is at least one tiny notch 110formed in the flexible disc 108. The present obturator 100 has twonotches 110 located along the edge of the flexible disc 108 anddiametrically opposed from each other. However, any number of notchesmay be provided on the flexible disc 108. The feature 109 may also beapertures (not shown) formed in an interior region of the disc 108,rather than notches disposed along the edge. The notches 110 prevent airin the distal end 22 of cannula 14 from being introduced into a vein orartery, when the cannula 14 is inserted therein. The notches 110 aresufficiently small to enable air in the distal end 22 of the cannulalumen 24 to escape out the proximal end 20, while preventing blood fromdoing the same. As the cannula 14 is inserted into a chamber of theheart or vessel, pressure from blood entering the first set of fluidapertures 28 forces any air trapped in the distal end 22 of the cannulalumen 24 through the notches 110, enabling air to escape out theproximal end 20 of the cannula 14.

The elongate member 106 of the obturator 100 may be a solid shaft orwire, or a hollow tube. It is preferred that the elongate member 106 andflexible disc 108 are integrally formed as a single piece, such as byinjection molding. However, the elongate member 106 and flexible disc108 may also be separate and distinct pieces, that are coupled togetherin a conventional manner.

As shown in FIGS. 12 and 13, the obturator 100 may include a sleeve 112that is injection molded directly therein. The sleeve 112, which ispreferably made of a malleable material, such as stainless steel, wrapsaround the exterior of the elongate member 106 and extends along atleast a portion of the length thereof. Since the sleeve 112 is made of amalleable material, the cannula 14, with the obturator 100 in place, maybe bent to a desired configuration, prior to insertion in the body, andwill maintain that configuration. In lieu of the sleeve 112, a malleablewire or rod (not shown), disposed inside the elongate member 106, willalso provide such a pliable structure.

The obturator 100 preferably further includes a stop 114 and a collar orgrip 116 as shown. The stop 114 is located on the elongate member 106,adjacent the proximal end 102, and limits the depth of insertion of theobturator 100 in the cannula lumen 24 to prevent damage to either theflexible disc 108 or the distal end 22 of the cannula 14. In thepreferred embodiment of the obturator 100, the stop 114 is conical inshape and includes a flat surface 118 and an inclined surface 120. Itshould be noted, however, that other configurations for the stop 114 maybe envisioned. The inclined surface 120 of the conical stop 114 extendstoward the distal end 104 of the elongate member 106, while the flatsurface 118 is located proximally of the inclined surface 120. When theobturator 100 is fully inserted in the cannula 14, the stop 114 abutsthe proximal end 20 of the cannula 14, with a portion of the inclinedsurface 120 being received in the cannula lumen 24.

The grip 116 is provided at the proximal end 102 of the obturator 100and is coupled to the elongate member 106. The grip 116 extends beyondthe diameter of the elongate member 106 and enables a user to grasp theobturator 100 and remove it from the cannula 14. The grip 116, stop 114,elongate member 106 and flexible disc 108 of the obturator 100 arepreferably injection molded as a single, integral piece. However, asdiscussed above, two or more pieces of the obturator 100 may be separateand distinct and may be coupled together in a conventional manner.

The flexible disc 108 of the obturator 100, the foam member 96 of theobturator 90, and the expandable balloon 78 of the obturator 76 are onlythree examples of expandable means provided on the obturator to permitpassage of the distal end of the obturator through the confines of thelumen and still capable of restricting the flow of fluid through thelumen of the catheter. It is understood that any other means whichaccommodate the varying diameters fall within the scope of theinvention.

The preferred method for forming the cannula 14 according to theinvention comprises the steps of extruding a circular length of tubing.Preferably, tubing is formed from silicone or polyvinyl chloride.Depending upon the particular application, a helically wound spring maybe received on the inside of the hollow tube and either be adhesivelyfastened therein or integrally molded therein. Next, the tubing is cutto the desired length, and then the non-circular portion is formed bypositioning the length of the tube between two opposed platens and thencompressing the two platens a sufficient distance to obtain the desirednon-circular or oval-shaped configuration. Once the spring has beenplastically deformed, it will retain the pliable cannula body in theoval or non-circular configuration. Finally, the luer connector and flowaperture member are mounted to the proximal and distal ends thereof. Thecannula 14 can be compressed to create the non-circular configurationprior to or subsequent to mounting of the elements on the proximal anddistal ends thereof. In the event that two different non-circularportions are formed along the length of the cannula, then the step ofcompressing the cannula body between two opposed platens is repeated, asnecessary, for the additional non-circular sections.

With the rapid evolution of surgical procedures which minimize the sizeof the access aperture cut into the patient, the known, conventional,surgical tools such as cannulas, vents, sumps, or suction tubes must beadapted to accommodate such advances. The non-circular cannula accordingto the invention is one such modification which assists the surgeons inachieving the goal of minimizing the wound size for a variety ofsurgical procedures. This advantage is accomplished without adverselyaffecting the fluid flow rate through the tubing or otherwise adverselyaffecting the performance of the tubing.

Reasonable variation and modification are possible within the spirit ofthe foregoing specification and drawings without departing from thescope of the invention.

What is claimed is:
 1. A method of positioning a fluid conductingcannula in a body, the method comprising the steps of: providing acannula having a proximal end, a distal end having a circularcross-section, a lumen extending between the proximal and distal ends, afirst portion having a non-circular cross-section, and at least onefluid aperture formed adjacent the distal end; inserting an obturator inthe lumen of the cannula, the obturator including an elongate member anda flexible disc, the elongate member having a proximal end and a distalend, the flexible disc coupled to the distal end of the elongate memberand substantially restricting the flow of fluid, entering the at leastone fluid aperture, through the lumen; providing a percutaneous aperturein a body; inserting the distal end of the cannula into the body throughthe percutaneous aperture; and positioning the cannula so that the firstportion resides within the percutaneous aperture.
 2. A method accordingto claim 1, further comprising the step of flexing the flexible discduring insertion of the obturator in the first portion of the cannula.3. A method according to claim 1, wherein the obturator includes a stopadjacent the proximal end of the elongate member, and wherein theobturator is inserted in the cannula until the stop abuts the proximalend of the cannula.
 4. A method according to claim 1, wherein theobturator includes a grip at the proximal end of the elongate member,and further comprising the step of removing the obturator by the gripafter the cannula has been inserted into the percutaneous aperture.
 5. Amethod according to claim 1, wherein the percutaneous aperture is ananterior thoracotomy.
 6. A method according to claim 1, wherein thepercutaneous aperture is a mini-sternotomy.
 7. A method according toclaim 1, wherein the first portion has an oval cross-section.
 8. Amethod of positioning a fluid conducting cannula in a body, the methodcomprising the steps of: (a) providing a pre-assembled cannula assemblyincluding: a cannula including a proximal end, a distal end having acircular cross-section, a lumen extending between the proximal anddistal ends, a first portion having a non-circular cross-section, and atleast one fluid aperture formed adjacent the distal end; and anobturator disposed in the lumen of the cannula, the obturator includingan elongate member and a flexible disc, the elongate member having aproximal end and a distal end, the flexible disc coupled to the distalend of the elongate member and substantially restricting the flow offluid, entering the at least one fluid aperture, through the lumen; (b)providing a percutaneous aperture in a body; (c) inserting the distalend of the pre-assembled cannula assembly into the body through thepercutaneous aperture; and (d) positioning the cannula so that the firstportion resides within the percutaneous aperture.
 9. A method accordingto claim 5, further comprising the step of flexing the flexible discduring insertion of the obturator in the first portion of the cannula.10. A method according to claim 5, wherein the obturator includes a stopadjacent the proximal end of the elongate member, and wherein theobturator is inserted in the cannula until the stop abuts the proximalend of the cannula.
 11. A method according to claim 8, wherein theobturator includes a grip at the proximal end of the elongate member,and further comprising the step of removing the obturator by the gripafter the cannula has been inserted into the percutaneous aperture. 12.A method according to claim 8, wherein the percutaneous aperture is ananterior thoracotomy.
 13. A method according to claim 8, wherein thepercutaneous aperture is a mini-sternotomy.
 14. A method according toclaim 13, further comprising the step of flexing the flexible discduring insertion of the obturator in the first portion of the cannula.15. A method according to claim 13, wherein the obturator includes astop adjacent the proximal end of the elongate member, and wherein theobturator is inserted in the cannula until the stop abuts the proximalend of the cannula.
 16. A method according to claim 13, wherein theobturator includes a grip at the proximal end of the elongate member,and further comprising the step of removing the obturator by the gripafter the cannula has been inserted into the percutaneous aperture. 17.A method according to claim 13, wherein the percutaneous aperture is ananterior thoracotomy.
 18. A method according to claim 13, wherein thepercutaneous aperture is a mini-sternotomy.
 19. A method according toclaim 8, wherein the first portion has an oval cross-section.
 20. Amethod of positioning a fluid conducting cannula in a body, the methodcomprising the steps of: providing a cannula having a proximal end, adistal end having a circular cross-section, a lumen extending betweenthe proximal and distal ends, a first portion having an ovalcross-section, and at least one fluid aperture formed adjacent thedistal end; inserting an obturator in the lumen of the cannula, theobturator including an elongate member and a flexible disc, the elongatemember having a proximal end and a distal end, the flexible disc coupledto the distal end of the elongate member, wherein the disc restricts theflow of fluid, entering the at least one fluid aperture, through thelumen, the disc allowing telescopic movement of the obturator throughthe distal end of the cannula; providing a percutaneous aperture in abody; inserting the distal end of the cannula into the body through thepercutaneous aperture; and positioning the cannula so that the firstportion resides within the percutaneous aperture.